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Hauntingly beautiful Venus, sometimes called Earth’s twin, as seen by the Galileo spacecrafts Solid State Imaging System on February 14, 1990, at a range of almost 1.7 million miles from the planet. Credit: NASA/JPL

Envision, a new Venus orbital mission proposal, has been selected for further study and possible launch by 2032, the European Space Agency (ESA) reports. If ESA selects the proposal as the fifth medium-class mission in its ‘Cosmic Vision’ program, the orbiter should enable planetary scientists to understand why Venus and Earth took such wildly different evolutionary paths.

Why Earth is a Valhalla and our sister planet Venus is a runaway greenhouse hellhole remains one of planetary science’s biggest mysteries. The standard view is that as the Sun's luminosity increased over time, what water Venus may have had dissociated into space, leaving the planet cloaked in dense Carbon dioxide and sulfuric acid clouds.

By no means is it certain that the planet most interior to the Sun would have still ended up like today’s Venus, Richard Ghail, Envision’s team lead and a senior lecturer in geology at the Imperial College London, told me.

“Venus may have had no water to start with, or its geological evolution might be different,” said Ghail.

Although Venus is now the very definition of inhospitable --- with 450-degree Celsius temperatures, a carbon dioxide-dominated atmosphere and surface pressures 92 times that of Earth --- some planetary scientists think at one point it may have been habitable.

And by measuring surface changes and volcanic gases via high-resolution one-meter scale imagery, Envision should help researchers scientifically-link Venus’ current geological activity with its atmosphere. This will help astronomers use our own Venus as a basis of comparison so that we can better understand a growing number of extrasolar Venus-type planets.

If selected, ESA says Envision would follow in the footsteps of its own successful Venus Express mission that focused primarily on atmospheric research. And the agency says Envision would also greatly improve on NASA’s successful 1990s Magellan radar mapping mission.

If approved, Envision would use an Ariane 6.2 launcher to begin a five-month journey to Venus, where the spacecraft would be gravitationally-captured. After six months of aero-braking, it would begin a four-year orbit some 259 kilometers above Venus’ surface.

As Ghail writes in the white paper, one mission goal would be to provide imagery from Venus at a resolution that would rival what’s currently available from Earth or Mars orbit.

Incredibly, Envision would be capable of detecting centimeter-scale surface changes that would enable the team to, as Ghail writes, characterize volcanic and tectonic activity, and estimate rates of weathering and surface alteration.

Envision would hopefully discover unknown structures buried below the surface as well as place better constraints on defining Venus’ interior structure by measuring the planet’s spin rate and spin axis variations.

Why not a lander mission?

Venus surface conditions make landing particularly difficult, says Ghail. However, he says that radar and communications technology have advanced so much in the last 20 years that we can learn an enormous amount about how Venus works from orbit. And at quite a modest cost. That is, on the order of half a billion dollars, not the two billion dollars Ghail says it would have cost a decade ago.

As for what we’re currently missing in understanding Venus?

“We really don’t understand the connections between the atmosphere, surface, and interior,” said Ghail. “Understanding these can tell us whether Venus is [geologically] alive like Earth, or dead like Mars.”

ESA says it expects to make a final decision on the Envision proposal’s future by 2021.